BANGKOK, Thailand -- Banning the trade in endangered wildlife can actually result in increased trade in the animals and their parts, a report published Thursday said.

The finding, reported in the journal Nature, is likely to fuel debate among conservationists who disagree over how to best curb the trade in endangered species.

Signatories to the Convention on International Trade in Endangered Species or CITES are due to gather in the Hague starting June 3 to consider revising the list of thousands of plants and animals whose trade is banned or regulated. The parties to CITES meet every three years.

"The most severe restriction that CITES can enforce is an explicit ban on commercial trade of wild species threatened with extinction," Philippe Rivalan, a researcher at the University Paris Sud, wrote in the Nature commentary. "We report here concerns that such bans can themselves lead to an increase in trade of vulnerable species."

Conservationists can recommend that CITES bans the trade in a particular endangered species. But because CITES can take between 240 and 420 days to actually implement the ban, the volume of trade in that species actually tends to rise during that period as traders try to beat the time limit.

Once the ban is imposed, prices can spiral upward.

The price of rhino horns on the South Korean market, for example, increased by 400 percent in the two years after CITES banned the trade in the items and the poaching of black rhinos rose. The study did not say when the ban was imposed.

"At the very least, our findings suggest that CITES authorities will need to use extra vigilance in controlling permits during transition periods and in adhering to quotas," Rivalan wrote.

Rivalan said CITES should work to speed up the listing process, so that conservation measures could be put in place before a species numbers drop to the point where a trade ban is necessary, he said.

A spokesman for the CITES Secretariat could not be immediately reached for comment.

Susan Mainka, a senior coordinator of the World Conservation Union's global program, disagreed with suggestions that implementation delays always result in a spike in illicit trade.

"For some species such as elephants, there has been a long string of listing proposals since 1989 that have not generated similar responses in illicit trade," she said.